OPINION:Signs of health and fertility, compatibility, sexual fidelity and humour all play a role when we look for a partner, writes WILLIAM REVILLE
What are the forces of attraction between men and women? This question has prompted much research, producing clear answers about some attractions and interesting hypotheses about others.
Evolutionary psychologists propose that the traits we recognise as beautiful in the opposite sex are really signs of health and fertility – characteristics of the greatest importance in a mate. For example, each sex finds bodily symmetry attractive in the other. We each begin life at conception as a single cell, the zygote.
This divides into two daughter cells, each of which divides in two, and so on and on. If everything goes perfectly, the born baby will have exact bilateral symmetry, but environmental pressures and mistakes frustrate perfect symmetry. However, a high degree of symmetry indicates that the bearer carries good genetic stock and is likely to make a fertile mate. So, evolution has programmed us to find symmetry attractive.
Randy Thornhill, an evolutionary biologist at the University of New Mexico, studied the attractiveness of symmetry, showing that men and women find symmetrical faces in the opposite sex more attractive than less symmetrical faces (Journal of Comparative Psychology, Vol 108, pp 233-242, 1994). He also found certain other facial characteristics are highly attractive to men and women.
The female sex hormone estrogen limits bone growth in the lower female face and in the brow, causing the eyes to appear larger. The male sex hormone testosterone develops a larger lower face and jaw in men and a prominent brow. These traits advertise reproductive health and rank as highly attractive.
Psychologist Devendra Singh, University of Texas, has shown the importance of the waist to hip ratio (WHR). Women whose waists are significantly narrower than their hips are very desirable to men – the ideal WHR is 0.7, but anywhere in the range 0.67-1.18 is good. Women find a WHR range of 0.8 to 1.0 attractive in men, but broad-shoulders are an extra plus.
WHR indicates the status of general health/vitality. Fat deposition in the body is determined by sex hormones and when the optimum amounts/proportions of sex hormones are produced, WHR naturally falls into the desirable range. People with WHRs in this range are less susceptible to diabetes, cardiovascular disease and cancer, and women in this range have less difficulty conceiving.
Pheromones are chemicals produced by the body to communicate information about reproductive quality. Pheromones act as powerful sexual attractants across the animal kingdom but play a lesser role in humans. Nevertheless smell is important. Thornhill offered sweaty vests from a variety of men to women. The women, especially when menstruating, found the scent of symmetrical men more attractive.
Initial attraction can be followed by feelings of love. Brain scans of people who recently fell in love show more activity related to love than to sex.
While visual and olfactory cues motivate initial attraction between the sexes, lasting relationships depend much more on behaviour. People are drawn to others who have similar attitudes and values. The psychologist JP Rushton studied heritable personality traits and found similar genetics plays a 34 per cent role in mate selection (Psychological Science, Vol 16, No 7, July 2005). He proposes that some combinations of genes work well together so finding a mate with similar genes to yours ensures favourable gene combinations are transmitted to your offspring.
How do people rank attractions when looking for a long-term mate? A Cornell University study of 1,000 people aged 15 to 24 (Proc National Academy Sciences, July 1st, 2003) ranked sexual fidelity as the most desirable characteristic, followed by physical attractiveness, family commitment, wealth and status.
Finally, humour is important. A man likes a woman who laughs at his jokes and a woman likes a man who makes her laugh. So, at the risk of inducing female readers to fall in love with me, here is a joke: A GP is having a fight with his wife at breakfast. In a rage he said “You are no good in bed either,” and stormed out of the house. Later, he felt sorry and phoned home. She answered after many rings and the irritated doctor asked “What took you so long to answer the phone?” She said “I was in bed.. He shouted “What the hell were you doing in bed this early?” She said: “Getting a second opinion.”
William Reville is an emeritus professor of biochemistry and public awareness of science officer at UCC. understandingscience.ucc.ie